This invention relates to automatic door operators for cold storage doors and the like having a hydraulic control system which provides a smooth operation at relatively high door speeds.
Automatic door operators are used to open and close doors which are mounted for swinging or sliding movement between open and closed positions. These doors, especially those available for cold storage purposes, are usually of the single panel or the bi-parting sliding type which include electro-mechanical drive systems comprised of a chain loop above the doors which is used to draw the doors between open and closed positions with an electric motor for driving the chain. The electric motor is controlled by an electric circuit which provides for the powering of the motor in the appropriate direction during the door opening and closing cycle. Electro-mechanical systems, however, may have a relatively short service life and must be frequently adjusted to compensate for the wearing of components. Also, this type of system may develop a sudden surge of torque from the electric motor upon start-up, and can also abruptly stop the motor when the door is fully opened or closed to result in undesirably rapid accelerations and decelerations that lack smoothness of operation.
There have also been provided hydraulic control systems for automatic door operators. U.S. Pat. No. 3,319,380 issued to Loftus for "Automatic Door Operator" shows a hydraulic system for opening and closing double swinging doors. He shows a pump driven by an electric motor which pumps hydraulic fluid from a reservoir through a check valve to an accumulator. From the accumulator fluid is fed through one of two electrically controlled valves to either of two hydraulic door operators. Loftus also shows an electric control circuit for controlling door operation. This type of hydraulic system, however, may be relatively slow for opening and closing cold storage doors which must be opened and closed rapidly to limit energy losses through the doorway.
It is also commonplace to use hydraulic or fluid cylinder-piston arrangements for operating doors that move in the plane of the door. For example, U.S. Pat. No. 3,619,946 issued to Crocker for "Automatic Door Operator" and U.S. Pat. No. 3,938,282 issued to Goyal for "Sliding Door Operator" show pneumatic operation in which a drive piston is slideably moveable within a cylinder upon actuation of a sensing device to open and close the doors. U.S. Pat. No. 2,298,542 issued to Potter et al. for "Door Operator" also discloses a hydraulic system for operating a reciprocal piston arrangement for a door. However, the drive pistons within the cylinders of the above arrangements match full door movement in length, and become excessively large for large doors.
The automatic door operator of the present invention includes an improved hydraulic control system which provides for smooth operation at relatively high door speeds by hydraulically cushioning the rapid start and stop of a door. The invention also provides increased service life through the use of hydraulic components that require less maintenance.